NASA's Swift Finds 'Missing' Active Galaxies

on January 20, 2011

Most large galaxies contain a giant central black hole. In an active galaxy, matter falling toward the supermassive black hole powers high-energy emissions so intense that two classes of active galaxies, quasars and blazars, rank as the most luminous objects in the universe. Thick clouds of dust and gas near the central black hole screens out ultraviolet, optical and low-energy (or soft) X-ray light. Although there are many different types of active galaxy, astronomers explain the different observed properties based on how the galaxy angles into our line of sight. We view the brightest ones nearly face on, but as the angle increases, the surrounding ring of gas and dust absorbs increasing amounts of the black hole's emissions.

What we see from an active galaxy's black hole depends on our viewing angle. Seen edge-on, the dense clouds of dust and gas around the central black hole prevent all but the most penetrating radiation to reach us. Artist's interpretation.

A newfound population of heavily absorbed active galaxies (orange curve) is thought to make the greatest contribution to the cosmic X-ray background (light blue). Both have similar spectral shapes and peak at similar energies. Adding in the known contributions from less-absorbed active galaxies (yellow and purple), appears to fully account for the background.

A newfound population of heavily absorbed active galaxies (orange curve) is thought to make the greatest contribution to the cosmic X-ray background (light blue). Both have similar spectral shapes and peak at similar energies. Adding in the known contributions from less-absorbed active galaxies (yellow and purple), appears to fully account for the background. No Labels